1. Field of the Invention
The present invention relates to a liquid storage apparatus for storing liquid, and to an image forming apparatus including this liquid storage apparatus.
2. Description of the Related Art
Various types of liquid storage apparatuses for storing ink to be supplied to an ink ejection head are known. An ink ejection head ejects ink supplied from the liquid storage apparatus toward an ejection receiving medium, such as paper, and forms images on the ejection receiving medium.
Japanese Patent Application Publication No. 2004-230890 discloses an ink cartridge comprising: a housing which defines a first fluid tank; an air management system having an attachment to be supported by the housing; and an expansible bladder which defines a second fluid tank and which is supported by the attachment within the first fluid tank. The expansible bladder is configured to expand to thereby increase the second fluid tank from a first volume to a second volume. The expansible bladder is fabricated from a material having a shape-memory to thereby bias the expansible bladder toward the first volume.
Japanese Patent Application Publication No. 2004-174815 discloses technology in which an elevator unit arranged inside an ink accommodating unit balances with the weight of an ink tank by means of a spring. More specifically, the ink tank is supported by a movable supporting member and a compression coil spring arranged between the ink tank and the movable supporting member. The ink tank is raised or lowered on the basis of the balance between the elastic force of the spring and the gravitational force on the ink inside the ink tank, so that the water head difference does not change even if there is a variation in the weight of ink.
In the technology described in Japanese Patent Application Publication No. 2004-230890, a slight negative pressure is generated in the ink chambers by using the expansion of the expansible bladder due to elastic deformation. Generally, in the case of an ink tank having a small capacity, the negative pressure can be created within an appropriate range until the ink is consumed. On the other hand, in the case of an ink tank having a large capacity, since the force generated by the elastic deformation increases, then the negative pressure exceeds the appropriate limit and the ejection state of the ink ejection head is thus affected, leading to a decline in print quality.
In industrial applications, various liquids having different physical properties, such as a specific gravity, viscosity, surface tension, and the like, are used. Possible examples of such liquids include: aqueous inks, oil-based inks, photocurable liquids, metal pastes, and the like. In the technology described in Japanese Patent Application Publication No. 2004-174815, if the liquid used is changed to another liquid having a different specific gravity, then the height of the ink tank depends on the balance between the elastic force of the spring and the gravitational force on the liquid, and therefore the position of the liquid surface will vary depending on the specific gravity of the liquid used.